Π-facial Diastereoselectivity Research Articles

On the origin of π-facial diastereoselectivity in nucleophilic additions to chiral carbonyl compounds. 2. Calculated transition state structures for the addition of nucleophiles to propionaldehyde 1, chloroacetyldehyde 2, and 2-chloropropionaldehyde 3.

The transition state structures for addition of LiH to 1, 2, and 3 are computed and analyzed at MP2/6-31G(d)//HF/6-31G(d). Three factors are found to be important for the relative energies of the transition state structures; (i) the conformational energy of the aldehyde; (ii) the interactions between the nucleophile and the aldehyde; (iii) the counter ion effect. The relative energies of the lowest lying transition state structures for addition of LiH and CN − to 3 leading to the major and minor product are not determined by the interactions between the attacking nucleophile and the aldehyde, but by the conformational energies of the aldehyde in the two transition states. The interaction between LiH and 3 is in fact more favorable in the transition state leading to the minor isomer.

On the origin of π-facial diastereoselectivity in nucleophilic additions to chiral carbonyl compounds. 1. Rotational profiles of propionaldehyde 1, chloroacetaldehyde 2, and 2-chloropropionaldehyde 3.

The conformational profiles for rotation around the CC(O) bond α and the energy minimum conformations are calculated for propionaldehyde 1, chloroacetaldehyde 2, and 2-chloropropionaldehyde 3 at MP2/6-31G(d)//HF/6-31G(d). The energy level of the LUMO is calculated as a function of α for 1, 2, and 3 and discussed in relationship to the Felkin-Anh model.

Transmission of polar substituent effects in the adamantane ring system as monitored by 19F NMR: hyperconjugation as a stereoinductive factor

A limited series of (E)- and (Z)-5-substituted adamant-2-yl fluorides 8 and 9, respectively, has been synthesized and characterized, and the 19 F chemical shifts have been measured in several solvents. A wide range of 19 F substituent chemical shifts (SCS, ppm) are obtained for the former system (ca. 9.1 (c-C 6 H 12 ), 9.6 (CDCl 3 ), and 11.8 (HFIP)) compared to the latter (ca. 0.6 (c-C 6 H 12 ), 0.7 (CDCl 3 ), and 2.3 (HFIP)). Factorization of the 19 F SCS into polar field (ρ F σ F ) and residual contributions ( 19 F SCS-ρ F σ F ) reveals the predominance of the latter solvent-independent component for the E fluorides (8). Comparison of 8 with a similar dissection of the 19 F SCS of 4-substituted bicyclo[2.2.]oct-1-fluorides 2 strongly suggests that the origin of the large residual contributions for 8 is «through-three-bond] electron delocalization or double hyperconjugation. The importance of this long-range electronic mechanism as a factor governing π-facial diastereoselection in 2,5-disubstituted adamantanes is discussed

Electronic control of π-facial diastereoselection. Electrophilic additions to 7-methylenenorbornanes

The approach of electrophiles to the sterically unbiased 7-methylenenorbornanes 2a–c can be remote controlled through electronic modification of 2,3-endo,endo-substituents.

ChemInform Abstract: π‐Facial Diastereoselectivity in Diels‐Alder Reactions of 2,5‐Dimethylthiophene Oxide.

Abstract2,5‐Dimethylthiophene (I) is treated with peracids to give the S‐oxide (II) mentioned in the title.

The regiochemistry and stereochemistry of 1,3-dipolar cycloadditions of 1-fluoro- and 1,1-difluoroallene

1,3-Dipolar cycloadditions of diazoalkanes, nitrones and nitrileoxides occur with high regioselectivity to 1,1-difluoroallene and fluoroallene, and with variable syn or anti π-facial diastereoselectivity with regard to additions to the latter. The roles of steric effects, frontier molecular orbital effects, electrostatic interactions and other factors which may be involved in determining the observed regioselectivity and π-facial diastereoselectivity are discussed.

π-Facial diastereoselectivity in Diels-Alder reactions of 2,5-dimethylthiophene oxide

A series of [4 + 2] cycloadditions with 2,5-dimethylthiophene oxide ( 2), generated in situ by peracid oxidation of 2,5-dimethylthiophene ( 1), are described. In all cases the syn adduct (with respect to the sulfoxide oxygen) is formed exclusively.